1. Field of the Invention
The invention relates to a speed controller (SC), and in particular to a speed controller with scales by which the position of a rotary button thereof can be determined.
2. Description of the Related Art
In line with higher integration of IC devices, the accuracy of the semiconductor process apparently becomes more important. Once any tiny error occurs in the semiconductor process, it causes a failure to the entire process, resulting in wafer damaging or scraping. Therefore, a great amount of cost is consumed.
Photolithography is one of the most important steps in the entire semiconductor process. Any regions, related to the structure of MOS transistors, for subsequent patterning and doping, are defined by photolithography. Basically, the photolithography includes three steps of coating, exposing and developing.
As to the coating, if a photoresist liquid is not uniformly sprayed onto a wafer, it can cause a failure to the entire semiconductor process.
Referring now to FIG. 1, there is shown a photoresist spray system. When coating a photoresist on a wafer, a photoresist liquid is evacuated from a photoresist bottle 10 via a filter 14 to spray onto a wafer 16 by a pump 12, wherein the filer 14 is used to filter the photoresist liquid. Furthermore, at least one speed controller 18, which is connected to the pump 12, can be adjusted to control the amount of the photoresist liquid sprayed. The performance of the entire photoresist spray system hinges on the capability of the speed controller 18.
Next, referring to FIG. 2, a speed controller according to the prior art is shown. The speed controller is an SMC 1200 series speed controller or an SMC 1400 series speed controller.
In FIG. 2, the speed controller 18 includes a housing 22 and a controller body 20 which is partly inserted in the housing 22. In addition, the controller body 20 has a rotary button 24 at one end thereof and a fixing button 26 under the rotary button 20. The rotary button 24 has stripes thereon which are designed to facilitate adjusting the amount of an air flow in the pump 12. The fixing button 26 is used to lock the rotary button 24 thereby to prevent unintentional adjustments.
As to the photoresist spray system, the amount of a photoresist liquid sprayed is one of main check items. For example, how many milliliters can be sprayed out in several seconds. In practice, it is found that the amount of photoresist liquid sprayed is inversely proportional to use time. This results from the filter 12 congested by photoresist particles. When the decrease in the amount of the photoresist liquid sprayed is found, an operator must adjust the speed controller 28 to allow the pump 12 to evacuate more amount of the photoresist liquid for compensation.
Assume that the photoresist spray system is installed with a new filter 14. Since the filer 14 is not congested by photoresist particles at all, a required amount of photoresist liquid sprayed can be easily obtained by just adjusting the speed controller 18 to a lower position. However, several weeks or months later, the speed controller 18 must be adjusted to a higher position for obtain the required amount of the photoresist liquid sprayed.
According to the prior speed controller 18, there is no way to predict the extent of the filter 14 congested. In general, the filer 14 is replaced with a new one by time, for example, once two months, regardless whether the filer 14 is still functional or not. As a result, it is possible that the filter 14, which cannot function well any more, is still used before the time for replacement, leading to a failure. This may be caused by an extra processing to have the filter 14 seriously congested or the unclean photoresist bottle 16 having congealed photoresist therein. Thus, a photoresist is poorly formed on the wafer 16.
Furthermore, the prior speed controller shown in FIG. 2 has no scales designed thereon. Therefore, an operator adjusts the speed controller only based on operating results. It seems reasonable to be widely used in the semiconductor process. However, there are disadvantages as follows.
(1) The speed controller is lack of previous alarm. If the system is already regulated, the speed controller should be adjusted within a certain range, so that the same results can be obtained under the same conditions. However, if the speed controller is abnormally adjusted, this implies that the system encounters a serous failure somewhere. Since no scales are designed on current-used speed controllers made by various manufacturers, the above-stated problem cannot be previously discovered and resolved.
(2) If the speed controller is adjusted only based on operating results, it seems to take the materials and products as experiments, resulting in the increase of manufacturing costs. An operator learns the speed controller should be adjusted only when failures are encountered. This is obviously unreasonable.
(3) The speed controller cannot be precisely adjusted.
(4) It is not convenient for engineering analysis.